To popularize the knowledge of wireless microphones and briefly introduce to you the performance of each frequency band, use occasions, etc.
The wireless microphone is divided into three frequency bands, the FM section. VHF section, and UHF section.
1. FM segment:
Everyone knows FM radio. The frequency of FM radio is 88-108MHz. The frequency of wireless microphones in the FM band is higher than 108MHz. Generally between 110-120MHz, so the FM radio signal will not cause interference to the FM radio microphone, but it will be interfered by other clutter. The advantages of FM wireless microphones are simple circuit structure and low cost, which is conducive to manufacturers' production. And its disadvantages are: poor sound quality, frequency will change with time/environment temperature, poor reception, disconnection often occur, the interference is large, and the sound will be interrupted when shouting into the microphone. The use occasions are generally very low requirements for use, and there are not much requirements for sound quality. FM wireless microphones can be used in this case where only sound is required.
2. VHF section
The VHF section is usually referred to as the V section, and the frequency is between 180-280MHz. Due to the high frequency, there is generally little interference. The frequency lock of crystal is adopted, and the situation of frequency conversion will not occur, and the receiving performance is relatively stable. V-band wireless microphones generally have two circuits.
The first circuit; the high-frequency part uses only a 2003 integrated IC. Including. Signal reception, radio frequency amplification, frequency mixing, frequency discrimination, etc. are completed in one step. Sensitivity is not high, the audio part uses 31101 line. The audio is compressed and expanded, and the sound quality is greatly improved compared to FM. The receiving performance has been improved by a notch. Its advantage is stable reception, and short-distance communication is rarely interrupted; but the disadvantage is that the high frequency part is not stable, the audio frequency response is not wide enough, and the effect of professional use is not ideal. Use occasion: general household, requiring relatively stable performance. The sound quality is decent in such occasions. This type of wireless microphone can be used.
The second circuit: the high-frequency part adopts discrete processing, high-frequency amplification, and intermediate-frequency amplification. Frequency mixing and frequency discrimination. Step-by-step processing, better effect, higher sensitivity, and more stable performance. The audio processing part adopts 571 circuit, which has better sound quality and wider audio frequency response. Its advantages are stable performance and good sound quality; use occasions for KTV halls, home use, small and medium-sized concerts, etc.
3. UHF section
UHF segment is generally called U segment. The frequency is generally 700-900MHz. There is basically no other external frequency that can interfere with such a high frequency, and most of the U-segment uses SMD components. The performance is very stable, there are generally three kinds of circuits in U. The audio reasonable circuit adopts the latest 571 circuit, and the sound quality is better;
The first type: single frequency. Similar to the V band frequency circuit, high frequency amplification, intermediate frequency amplification. Frequency mixing and frequency discrimination. Step-by-step processing, high-amplification is divided into several episodes for amplification, audio processing adopts 571 circuit design, and the sound quality is clear. Use occasions: when it is not satisfied with the V segment, the requirements for use are not very high. Or if there is interference in the environment where the V-segment machine is used, this type of machine can be used;
The second type: adjustable frequency type; this type of machine is controlled by a microcomputer program. The high-frequency oscillation is controlled by a phase-locked loop (PLL). Generally there are multiple channels adjustable. Thousands of adjustable frequency points are available for selection. Effectively avoid interference, multiple machines can be used at the same place at the same time without interfering with each other. If there is interference, adjust the frequency point to other frequency points to avoid interference, squelch control. The audio processing adopts a brand-new design with stable performance. Use occasions: this type of machine is used in many high-end KTV rooms. Small and medium-sized concerts. Or require multiple colleagues to use when singing, the effect is ideal;
The third type: diversity; the so-called diversity is diversity reception, one is single-frequency diversity. One is tunable frequency trial diversity. This type of machine has the functions of a U-segment machine, and each channel uses a two-way receiving circuit system. For example, there is a dead point in the receiving system of one channel, and the signal can be received in another channel, which effectively avoids the signal dead zone, greatly improves the technical level of the whole machine, and ensures the stability of the received signal and continuous reception. This type of machine is more advanced wireless microphone. The farthest use distance can reach more than 200 meters.
Use occasions: various large and medium-sized concerts. The use environment is very demanding and the use environment is more complicated. This type of machine is the best choice;
Since each manufacturer has different technical levels and different production processes, different manufacturers of the same model will also have different quality problems. So buyers must pay attention to this issue, and hope that through me, I can help you buy a wireless microphone suitable for your use. It is best to look at the professional knowledge before buying, so as not to let people mislead you.
To understand the performance characteristics of wireless microphones, it is necessary to first understand the basic terms of wireless microphones and the specific meaning of the main performance indicators. In addition to wireless microphones having the same audio indicators as wired microphones, there are also some unique terms and performance indicators, which will be introduced one by one below.
Squelch: When the wireless microphone receiver does not receive a signal or the signal is weak, it will automatically cut off the output signal in order to avoid output noise. This function is called squelch (Squelch). If there is no squelch function, or the squelch function is poor, noise will be emitted from the speaker speaker when there is no signal or weak signal. Noise will affect the sound quality, destroy the atmosphere of the scene, and even damage the sound reinforcement equipment.
Dead point: also known as dead zone or blind zone. During the movement of the wireless microphone, the signal received by the receiver will vary in strength due to the difference in distance, relative position, or obstacles. In some positions within the normal use distance, too weak signals will cause the squelch circuit in the receiver to act and cut off the output signal; and after leaving this position, it can be received and output normally. This position is called the dead spot or blind zone. When the wireless microphone approaches or exceeds the effective distance, dead spots will inevitably occur. If the circuit design is reasonable, there will be no sound when the dead spots occur; if the design or manufacturing is poor, there will be no normal sound, but noise .
Diversity reception: It means that the wireless microphone receiver can receive the signal of the same wireless microphone from two antennas respectively, and select the stronger signal through the internal circuit. In this way, the receiving dead zone can be largely eliminated, and the muting or dead-point noise can be avoided. There are two ways of diversity reception: antenna diversity and mid-amp diversity.
In the antenna diversity mode, there are two receiving antennas, a control circuit and a receiving circuit. When the received signal is weak during operation, the control circuit will automatically switch to another antenna.
In the mid-amp diversity mode, in addition to two antennas and a control circuit, there are two complete receiver circuits that work at the same time, and the control circuit tracks and switches to output a better audio signal. This method is better than the previous method because it tracks strong signals at any time, but the circuit is complicated and the cost is high. This kind of diversity is often referred to as dual tuning, true diversity, and so on. Generally, in important occasions such as live performances, studios, etc., products with dual-tuning true diversity must be selected to ensure that no dead spots occur within a practical operating distance.
Multi-channel: The carrier frequency of a general wireless microphone is fixed, and the user cannot change it during use. Since wireless microphones transmit sound signals through radio waves, when there are external signals that are the same or close to their carrier frequency in the working environment, interference will occur, which will reduce the receiving distance of the receiver, output noise, or even fail to receive it. The signal of the microphone.
In response to this situation, the manufacturer has developed a multi-channel wireless microphone system. The working frequencies of its transmitter (wireless microphone) and receiver are adjustable, so that users can change the carrier frequency of the system when encountering external frequency interference to avoid interference signals and work normally; in addition, if When multiple wireless microphones are used in the same venue, each microphone can be easily adjusted to a different working frequency, so that they do not interfere with each other and work in coordination. Most of the wireless microphones used in large professional stage performances are multi-channel systems, with 8 channels, 16 channels, or even more channels, of which 16 channels are the most common. Multi-channel systems generally use phase-locked loop (PLL) frequency synthesis technology, microcomputer control technology and other related technologies. Its production technical requirements, equipment requirements, production costs and product performance are much higher than other ordinary models.
At present, some products on the market are fixed frequency, but a batch of products of the same model can also be produced into products with different frequencies. Users can choose when buying, but after purchasing, they cannot adjust their working frequency during use. Some manufacturers This situation is also labeled "multi-channel", "32 channels can be chosen at will", this is inaccurate, or deliberately misleading consumers. This situation requires special attention. There are several ways to distinguish: one is to observe whether there is a switch or button to adjust the channel on the receiver panel; the other is to see whether the promotional materials or manuals are marked with "adjustable frequency" and "user can "Adjust the channel" and other words; the third is the actual operation to see if it is adjustable.
Signal-to-noise ratio: refers to the ratio of the original audio signal to the noise signal in the output signal when the receiver receives a signal of a specified strength (usually 60dB μV), expressed in decibels (dB). The larger the value, the purer the signal and the better the machine performance.
Receiving sensitivity: In a radio or walkie-talkie, the receiving sensitivity refers to the size of the minimum RF signal that needs to be input when the receiver outputs a signal with a specified signal-to-noise ratio. The smaller the value, the higher the receiving sensitivity of the receiver. In a wireless microphone, it should be expressed by the value of the input RF signal when the receiver is critically muted, because when the input signal is lower than the muting point and the receiver is in the muted state, no signal is output. For example, the receiving sensitivity of a product is marked as "-90dBm", which means that when the antenna input signal is lower than -90dBm (ie 7 μV), the receiver will enter the squelch state. Such marking can accurately reflect the receiver's receiving ability . Some products have sensitivity indicators similar to radios and walkie-talkies. For example, they are marked as "2 μ V/12dB", which means that when the antenna input signal is 2 μ V (ie -101 dBm), the receiver output signal can be A signal-to-noise ratio of 12dB is achieved. The signal-to-noise ratio of wireless microphones is required to be much higher than 12dB, so this marking method cannot correctly express the receiver's receiving capability.
RF output power: refers to the amount of signal energy transmitted by the wireless microphone transmitter to the space, usually expressed in milliwatts (mW), generally between 5 and 50 mW.
Effective working distance: refers to the maximum distance that the wireless microphone can transmit signals normally. Most of the parameters marked on the product indicate that it is in an open area or under ideal conditions. Because the actual transmission distance of the wireless microphone is affected by the actual environment, it cannot be accurately marked. Only indicators under open areas or ideal conditions can provide reference and can be compared with each other.
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